I have owned a mason 2x3 and now own a mason 2x4 with a blower. I agree with everything person25 said. I have built a wall like you did but I moved it back to within a couple inches of back wall. And than using fire brick I built a ramp to it. What I have found with my blower on 2x4 is that ash will build the ramp even higher while boiling.
110 taps W.F Mason 2x3 and two turkey friers for finishing
2011 expanding to a Mason 2x4 with a blower increasing taps to about 200
2011 Hurricane Irene rips thru my small sugar bush cost me to lose 20% of taps
2014 I have reworked my lines for 2014
32 taps on 5/16 line with check valves
57 taps on 3/16 line with check valves
55 buckets with total tapped trees of 144